Answers

Such a FUN topic you've chosen.

If you're on city sewer, and if it's not gravity flow all the way,
you might likely have problems if your house is in a low (terrain
wise) area. Call the city sewer folks and find out where the pumping
stations are if you're curious. If your house is in a lowlying area,
move your food storage out of the basement... . And look for the
nearest manhole cover (it'll come out there too). YUCK!!!!!! Needless
to say, the disease problem potential would be awesome... .

By the way, if your water is off for a while (as in several days)
make sure your drain traps stay full by pouring a couple of cups of
water down them every so often. The water in the traps serves to keep
sewer /septic system gasses from backing up through the drains. The
stuff you have to keep in mind for y2k is overwhelming, isn't it??

I was told by my uncle, a plummer, that newer houses have a safety
valve in the sewer to prevent back-up. Is this enough to prevent
problems like the ones described? We are getting a composting toilet
and are planning not to have to go outside if we have the worst-case
scenario, to avoid coming in contact with other peoples' waste.

Here in California, only low-flow toilets are sold and installed in
homes. We have problems right now with sewers not flowing all the way
to the treatment plants. We have to flush our toilets 3 times just to
get the sewage down the pipes. I know several wastewater engineers
who I have spoken with that are concerned about the current problem,
and the potential for further problems if the sewer systems completely
fail. We are lucky that we are sitting on top of a mountain.

Sewer pipes do have reverse flow traps built into them. Ours is just
before it leaves the cellar. It consists of a ball that floats and
whatever is flowing in the wrong direction will push the ball up and
into a seat, a narrow part of the pipe, thereby stopping the flow.

As for the sump pump, if it stops doing its job because of no
electric, you'll have another problem with lots of water in the
basement. The sump usually doesn't run much in the winter but spring
when all the snow is melting, the sump fills quickly.

We have been tossing this around. There are 12 volt pumps one could
use with a car battery. But for a more dependable solution we came
up with using with the pool pump run by bicycle power, or better, the
lawnmower engine as long as there was gasoline. If the sump wasn't
filling very quickly you could set up one of those radio shack tone
alarms to go off when the water raised to a certain point. Just
start the engine for a couple of minutes and empty the sump. You'll
no doubt have to prime the pump first. A long intake hose looped out
on the cellar floor will hold sufficient prime water to keep it going
while you start the pump and drop the end of the hose into the sump.

Come down to that, if the power fails for the force mains, the pumps that fill the reservoirs will likely go down too. The water supply won't last much beyond that, depending on the reservoir serving the area.

But flush water to clear a toilet can come from the used wash water in from a sink, a bucket, the tub, or anything else, including the creek outside (except for those in the great frozen northland who have to use an ice drill to look at fish in the wintertime ....)

The disposal end of your house plumbing is strictly gravity.

Note: I have never trusted a check valve to stop reverse flow water -- especially if it contains sewer gases, poisons, or other unpleasantries. Slow moving fluid, even if there no particles to physically block open the check valve, leaks past those things very easily. Don't trust the check valve to keep sewage out.

Low areas in the service area are most likely to be hurt - much less so a little higher up.

Most likely, if you have never (even in the worst floods) had water backed up, it may not this time, because a sewage plant is likely to fail "open" and discharge raw sewage uncontrolled downstream of the plant. Unless the sewage plant itself goes down so that nothing flows out, (instead of everything flows out) - this would polute "upstream water" in the pipes.

The problem here in flat FL is that the county has to use "lift stations" to get sewage to the treatment plants. Needless to say these use electric pumps to "lift" the stuff. The County emergency guy says in the event of power failure, the lifts stop lifting. Everytime some one flushes on your sewer line it goes down hill to the lift station and then starts backing up in the main sewer line and then into the lines of the homes lowest on the line and then into the homes NEXT lowest on the line. See where this is going? At some point when the guy in the house HIGHESTon the line flushes, the stuff just stays in his toilet (or overflows) but ALL the rest of the homes down hill are full of S---T already. You need to be able to close off your house line from the main. You won't be able to flush but the S---T will stay out of your home until the lift stations start working again. Can anyone spell LATRINE?

There aren't any "sewage" cutout lines in any plumbing system in any county ot metro area in any area of the country I'm aware of. People just don't make them, install 'em, or expect to install 'em.

Florida? New Orleans? Any place "low enough" to maybe backup from upstream sewage?

Just to put one in in you'd need to excavate the edge of your slab (no cellars or crawl space, right?) and get access to the sewage pipe, cut the pipe, install the new valve (gate valve probably, ball valve might work, but there aren't any for residential use I'm aware of, can't use a regular globe valve else the flushed particles will clog the valve), then provide a manhole or handhole access to the cutoff handwheel so you could shut it off, if/when needed.